Collective bargaining in higher education differs somewhat from bargaining by primary and secondary school teachers. The National Labor Relations Act applies to many private institutions of higher education, which usually have much higher revenues and many more employees than private schools at the primary or secondary level. In many states, the same statutes that govern bargaining at the primary or secondary level govern collective bargaining in higher education. In other states, however, the statutes prescribe different rules with respect to state universities than they do with school districts. Governance of a public university is often much more complex than governance at a primary or secondary school, and the interests of the employees is often much more diverse among university faculty members and other employees than the interests of high school, middle school, or elementary school teachers and employees. Whereas a primary or secondary school may require only a minimal number of bargaining units, a large university may require several bargaining units to represent the various interests of the employees of the university.